What actually does an uncoupling membrane do?

Discussion in 'Shower & Bathtub Forum & Blog' started by jadnashua, Apr 4, 2014.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    It's made out of the same plastic as the other Ditra uncoupling mats, if that helps. Once installed, and you've filled it up with the thinset and set the tiles, the actual flexibility of the mat is what provides the stress-relief in the lateral plane. The air space in the towers is what allows it to move horizontally without cracking the thinset or breaking a tile(not vertically)- IOW, it MUST be flexible to obtain the uncoupling. Keep in mind, you still have the rigid tile bonded to the thinset that keep the towers in place, only deflected as a whole assembly (tile/thinset). The areas where the thinset goes to the base of the mat are what provide the vertical support, and their spacing is the reason why there is a minimum tile size requirement - the tile needs to be supported by a minimum number of thinset towers to provide adequate compressive strength, only limited by the compressive strength of the mortar used. If you don't wear kneepads when working on your knees, you might want to use a kneeling pad, but you won't hurt the mat in the process - it will be more comfortable for you. That's pretty much true for any uncoupling mat.

    That is one reason why, as opposed to say a crack isolation membrane which needs to span a ways over a crack to have enough flexibility to actually isolate it, an uncoupling membrane does that from its inherent structure over the entire mat, regardless of its size - things can move any direction laterally, independent of the subfloor or slab and the width (contrary to what John thinks) has no impact on its decoupling capabilities.

    Any test trying to exceed the industry standards with any mat are misleading and mostly useless...all membranes of this type must meet a minimum of 50psi to pull it off the substrate (the fleece attachment layer will fail first), and that will be the weakest link in the system. The only way to determine how well it works for uncoupling would be to install multiple strain gauges in the sandwich, and measure how much stress can be applied before either a tile or a grout joint fails or breaks. No backyard test is going to do that, and with crude measurement tools, is mostly a joke and pointless. These things are designed for use on a floor, and you're not going to have something yanking the tile up (gravity doesn't work that way) or pull it sideways. Yes, the tile and the substrate move separately, but that's the whole reason for an uncoupling membrane, to isolate them. For any practical installation, it far exceeds anything needed. It does NOT reduce the need for expansion joints IN the tile - it only works between the substrate and the tile - the tile's expansion can exceed the strength of thinset regardless of whether it is attached via bonding directly or whether it is placed on an uncoupling membrane. The beauty of the uncoupling membrane is that thinset does NOT stick to it (at least on Ditra - why one would want fibers as part of the tile bond is beyond me, and probably mostly to avoid patent issues - they state that they tear in the process, anyways, so why have them!).

    The whole concept of you must use a modified thinset for attaching porcelain or glass IS true, IF you direct bond them in many cases. When using an uncoupling mat (and the installations from centuries ago used their version of an uncoupling mat - a packed sand bed - no cement, just sand and their glass and porcelain installs work just fine), you have probably at least a 300% stronger bond to the tile than any lateral stress that can be applied to it. IOW, it isn't going to come off unless you try to destroy it!
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    FWIW, the rating categories of the Robinson floor test are: residential, light, moderate, heavy, and extra heavy. The description of the test result describes what they deem each level to be suitable for.

    Ditra heat, like any uncoupling membrane, will give different results based on the tile, the substrate, and some random factors based on the wood involved, and the fact that humans and nature aren't perfect, but look at test report TCNA-415-13, with OSB, 19.2"OC, and a 12x12" porcelain tile, it received an EXTRA HEAVY rating...the highest they give, (and better than the heavy you're so proud of) and also, Schluter pays for multiple tests, and only lists a rating that passes that level for EACH test sequence...some get one good rating, and use that, ignoring the others...nothing's exactly the same - Schluter wants it to work, when they say it will, regardless as long as you install it the way the say (something, you have a problem doing). They ran a bunch of tests using natural stone over Ditra with a single layer of plywood...the majority of the time, it passed the tests with a reasonable margin, but not 100%. As a result, they do not warrant natural stone over a single layer of ply...the result of being conservative and wanting to know the user can ALWAYS get it to work, backed up by testing, when installed as they say. They do not like 'ifs'...if it doesn't work, they either fix it during design, or don't sell it. That doesn't mean they don't make changes along the way based on feedback or technical advances or production methods, but the products have to continue to work as advertised WHEN INSTALLED ACCORDING TO THEIR INSTRUCTIONS (again, which John Whipple has a big problem with, thinking his way is better - sort of the NIH mindset some companies have (not invented here - if I didn't do it, it can't possibly be as good).

    Maybe a little research, rather than the knee-jerk, typical of you, reaction may be worth considering.

    For those of you who may have been following this since the beginning, John Whipple doesn't like me, dislikes anything I say, and tries to pick apart any bit of it. He now, also dislikes Schluter because they told he they were not pleased with his unscientific comparisons, incorrect installations, and various comments about their products...talk about vindictive. Schluter has been in business for decades, products sold around the world, has innovated many of the advances in materials and techniques for tile installations. That I admire them, is partly because I'm an engineer, retired, having worked in designing, testing, and teaching troops how to use various missile systems for over 30-years helps me to recognize and appreciate that innovation and professionalism Schluter has for their products and how they treat their customers. In my job, failure to do what we said could mean thousands of lives lost and billions of dollars in property damage - IOW, you have to get it right the first time. My experience is that Schluter has the same attitude, but like anything, you have to use it as it was designed. I have used products from other companies, and some are as good, some are lousy, and some have no overlap, so there is no choice. I have no agenda here, I do not get any commissions, or rebates, or financial incentives to post anywhere. John has an interest in making himself look good (and an obvious ego) and promote his business, and anyone that challenges something he says is an enemy...I think you get what I mean.

    Uncoupling mats work. You may not always need one. To me, if your choice was a cbu or an uncoupling mat, the uncoupling mat would always win, even if it cost more. For a pro, because of the speed and ease of installation, more than a few pros I know will only install cbu if the customer insists - the difference in cost of materials is easily covered in the time savings (labor is often a significant portion of the job)...the customer is always right, even when they're wrong. When the probability of failure isn't a big issue, yes, either will work, and one may be overkill (but John LIKES overkill, if you follow any of his methods). There are times when an uncoupling mat will be the only sane solution, but in many cases, you can get by without one.
     
    Last edited: Apr 10, 2014
  3. MACEOD

    MACEOD New Member

    Joined:
    Jul 1, 2017
    Location:
    Inverness, FL
    I hope someone is still out there. I have a FL slab home with several structural cracks discover after pulling up the carpet. The cracks range from between one-eighth and one-quarter inch, I am filling the cracks with a high-quality epoxy resin prior to having a professional level the floor. I want to isolate the slab from the tile to preclude the transition/formation of new cracks should the slab develop a new crack. The new tiles are large format so any movement will be problimatic. From all the reading I have struggled through, I require a crack isolation membrane.......yes/no? If so what are the top choice for my situation?
     
  4. MACEOD

    MACEOD New Member

    Joined:
    Jul 1, 2017
    Location:
    Inverness, FL
    OMG i am now posting a reply to contradict myself...............so maybe it is an uncoupling mat I need and possibly a beanie with a propeller to whisk me away. You guy talk pro to pro, I am on the other hand an wanna-be. Take pity, give me some good advice!
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    First, if those cracks have any vertical height difference, you should NOT tile the surface at all! If they are spreading cracks without any vertical height differences, you can tile it but, an uncoupling membrane is not going to isolate the tile from the cracks...for that, you need a crack isolation membrane. Uncoupling are different than crack isolation. In some situations, you might want both.

    Industry standards call for 'honorning' the crack with a soft joint in tile above the crack. That can be an engineered joint or a grout joint filled with a caulk. Depending on the area's use, there are different 'caulk-like' materials that have different hardness, and thus service life. Some of them are available in matching grout colors, but not all.
     
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